Solenoid valve with nozzle

ABSTRACT

A fuel injection valve having a hollow plastic nozzle with a discharge orifice at its front end, and a plastic bobbin with a hollow barrel and spaced flanges, the nozzle and barrel being in spaced alignment, and a coil surrounding the barrel between the flanges. A valve plunger in the nozzle is movable between closed and opened positions and has a front end which closes the orifice in the closed position, the plunger forming a first fluid passage communicating with the orifice. A magnetic casing surrounds a part of the nozzle and the bobbin and coil, and holds the nozzle and bobbin in assembled relation, the casing having a portion bridging the space between the nozzle and barrel. An armature is attached to the rear end of the plunger and has a portion extending into the space between the nozzle and bobbin and defining a first, fixed airgap with the bridging portion of the casing, the armature also forming a second fluid passage communicating with the first passage. A magnetic core is positioned in the barrel and forms a second airgap with the armature in its closed position, the core, casing and armature forming a magnetic circuit for the coil. The core forms a third fluid passage communicating with the second passage, and a spring normally biases the armature and plunger to the closed position. The core is secured to the casing, and the casing includes an inlet conduit communicating with the third passage.

United States Patent Dixon et al. 1 May 8, 1973 [54] SOLENOID VALVE WITH NOZZLE [57] ABSTRACT [75] Inventors: Thomas E. Dixon; Robert W. Herr; A fuel injection valve having a hollow plastic nozzle Edward D. Sig], all of Fort W with a discharge orifice at its front end, and a plastic- Ind. v bobbin with a hollow barrel and spaced flanges, the nozzle and barrel bein in s aced ali nment, and a [BI Asslgnee: Bowmar Instrument Corporation coil surrounding the birrel Eetween fhe flanges. A Fmt'wayne valve plunger in the nozzle is movable between closed 22 Fil d; F 24, 1972 and opened positions and has a front end which closes the orifice in the closed position, the plunger forming [2] 1 Appl' 2 18 a first fluid passage communicating with the orifice. A 1 magnetic casing surrounds a part of the nozzle and the 52 11.5. (:1 ..239/585, 251/139 bobbin and coil, and holds the "M116 and bobbin in 51 1111. c1. .3051) 1/32, Fl6k 31/02 assembled relation, the casing having a Portion [58] Field of Search ..251/139; 239/585 bridging the Space between the nozzle and harrel- Ah armature is attached to the rear end of the plunger [56] References Cited and has a portion extending into the space between the nozzle and bobbin and defining a first, fixed airgap UNITED STATES PATENTS with the bridging portion'of the casing, the armature also forming a second fluid pass-age communicating 2 with the first passage. A magnetic core is positioned in 2:6l9:116 11/1952 Ralstoriiu I ..2 5 l/139 X t e barrel and forms a second airgap with the arma- 3,412,970 11/1968 Robarge ....251/139 X in its Position them, casing and 3,592,228 7 1971 Kukum inato et al. ..251 139 x forming a magnetic Circuit for the Coil- The Core w forms a third fluid passage communicating with the Primary Examiner Robert ward, JL second passage, and a spring normally biases the ar- Att0mey Hamld Hood at mature and plunger to the closed position. The core is secured to the casing, and the casing includes an inlet conduit communicating with the third passage.

17 Claims, 10 Drawing Figures 2a 7a m 12 I I28 I Y 94 3 I46 1 1, A 14 1a I52 95 B156 60 anemones/onion lw wuww www I 42 /V//// ///A-! \x x \x rt }t s I 4o 4! 95 I26 58 4 I le M 2-)] 3a 3a1 72 98 PATENTED HAY 81973 SHEET 1 BF 3 SOLENOID VALVE WITH NOZZLE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to solenoid valves, and more particularly to a fuel injection valve.

2. Description of the Prior Art In one type of solenoid valve adaptable for use as a fuel injection valve, sometimes referred to as a thruway valve, the operating coil surrounds a central passage or conduit having an orifice and valve seat therein. The armature is positioned in the central passage being spring-biased normally to close the orifree, and being moved to open the orifice upon energization of the coil. US. Pat. Nos. 3,529,806, 3,450,353, 3,420,260, 3,241,768, 3,231,233, 3,125,321, 3,001,757 and 3,004,720 are typical of this type of construction.

In a fuel injection valve, the degree of opening of the valve orifice and the duration. of the opening control the fuel flow, close control of the fuel flow being desirable for optimum engine performance. Prior art fuel injection valves known to the present applicants do not provide for convenient adjustment of the rate of opening and closing of the valve subsequent to its final assembly. It is further desirable to provide a fuel injection valve which lends itself to automated fabrication and assembly.

, SUMMARY OF THE INVENTION A solenoid valve which comprises a hollow nozzle member formed of non-magnetic material and having a front end with a discharge orifice formed therein, and an open rear end. A bobbin member formed of nonmagnetic material is provided including a hollow barrel portion having open front and rear ends, and spaced flange portions formed on the barrel portion with a coil surrounding the barrel portion between the flange portions. The nozzle member and the barrel portionare in alignment with the rear end of the nozzle member spaced from the front end of the barrel portion. A-valve plunger is positioned in the nozzle member axially movable between closed and opened positions and having a rear end and a front end which closes the orifice in the closed position, the plunger forming atirst fluid passage communicating with the orifice in the opened position. Casing means formed of magnetic material surrounds a part of the nozzle member, and the bobbin member and coil, for holding the nozzle member and bobbin in assembled. relation, the casing means having a portion bridging the space between the rear end of the nozzle member and the front end of the barrel portion of the bobbin member. A disc armature member is provided at the rear end of the plunger and movable therewith, the armature member being formed of magnetic material and having a portion extending into the space and defining a first, fixed airgap with the casing means bridging portion, the armature also forming a second fluid passage communicating with the first passage. A core member is provided formed of magnetic material, the core member being positioned in the barrelportion and forming a second airgap with the armature in the closed position, the core member, casing means and armature forming a magnetic circuit for the coil so that the armature is moved toward the core and the plunger is moved to the opened position upon energization of the coil, the core also forming a third fluid passage communicating with the second fluid passage. Spring means is provided normally biasing the armature and plunger to the closed position, and means are provided for securing the core to thecasing means. The casing means includes an inlet conduit portion communicating with the third passage whereby fluid flows from the inlet conduit through the passages and orifice upon energization of the coil.

In the preferred embodiment, means are provided for adjustably connecting the core to the securing means thereby selectively to adjust the second airgap, the spring means acts between the armature and the securing means, and means is provided for adjustably connecting the securing means to the inlet conduit thereby selectively to adjust the spring rate of the spring means.

It is accordingly an object of the invention to provide an improved solenoid valve.

Another object of the invention is to provide an improved solenoid valve particularly adapted for use as a fuel injection valve.

A further object of the invention is to provide an improved solenoid valve including means for selectively adjusting the operating characteristics of the valve.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view, partly in cross-section and partly broken away, showing the preferred embodiment of the invention;

FIG. 2 is a cross-sectional view taken generally along the line 2--2 of FIG. 1;

FIG. 3 is a cross-sectional view taken generally along the line 3-3 of FIG. 1;

FIG. 4 is a cross-sectional view taken generally along the line 4--4 of FIG. 1;

FIG. 5 is a cross-sectional view taken generally along the line 5-5 of FIG. 1;

FIG. 6 .is a side view, partly in cross-section and partly broken away, showing another embodiment of the invention;

FIG. 7 is a cross-sectional view taken generally along the line 77 of FIG. 6;

FIG. 8 is a cross-sectional view taken generally along the line 88 of FIG. 6;

FIG. 9 is a cross-sectional view taken generally along the line 99 of FIG. 6; and

FIG. 10 is a cross-sectional view taken generally along the line IO--- 10 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, the preferred embodiment of the invention, generally indicated at 12, comprises nozzle member 14, valve plunger 16, bobbin l8, casing member 20, core member 22, armature member 24, inlet conduit member 26, core mounting member 28, spring 30, and coil 32.

Nozzle member 14 is formed of suitable non-magnetic material, preferably a plastic material such as glass-filled nylon. Nozzle member 14 has a reduceddiameter front end 34 having discharge orifice 36 formed therein, and enlarged body portion 38 having cavity 40 therein communicating with orifice 36. Valve seat 42 is formed between orifice 36 and cavity 40. Radially spaced fingers 44 extend rearwardly from rear end 46 of body portion 38.

Valve plunger 16, also formed of non-magnetic material, preferably of plastic such as glass-filled nylon, is positioned in cavity 40 of nozzle member 14 and is movable axially therein between a closed position with its front end 48 seated against valve seat 42, as shown, and an opened position with front end 48 spaced rearwardly from valve seat 42. As best seen in FIG. 2, valve plunger 16 has flattened sides 50 spaced from the inner wall of body portion 38 of nozzle member 14 thereby to provide fluid passages 52 communicating with orifice 36 when valve plunger 16 is in its open position.

Disc armature 24 is formed of suitable magnetic material and has a central opening 56 seated on and adhesively secured to plug 58 at rear end 60 of valve plunger 16. Armature 24 has cut-out portions 62 formed therein which define portions 64 extending radially outwardly between fingers 44 integrally formed on rear end 46 of body portion 38 of nozzle member 14.

Bobbin 18 is formed of suitable non-magnetic material, preferably a plastic material such as glassfilled nylon. Bobbin member 18 comprises an elongated barrel portion 66 having a central opening 68 formed therethrough, and axially spaced flange portions 70, 72. Barrel portion 66 is disposed in axial alignment with nozzle member 14 with its front end 74 abutting the ends of fingers 44. Coil 32 is wound on barrel portion 66 between flange portions 70, 72, and may have case 76 formed of suitable plastic material molded thereover in order to seal the coil against any fluid which may leak past the O-ring seals to be hereinafter described.

Casing member formed of suitable magnetic material has rear portion '78 surrounding bobbin 18 and coil 32, and front portion 80 surrounding and embrac-.

ing body portion 38 of nozzle member 14. Flange portion 82 in front portion 70 engages the front wall 83 of body portion 38 of the nozzle member 14, O-ring seal 84 is provided between flange 82 and body portion 38 of nozzle member 14, and O-ring seal 86 is provided between front portion 80 of casing 20 and barrel portion.66 of bobbin 18, as shown. It will be observed that section 88 of front portion 80 of casing member 20 bridges the space defined by fingers 44 into which portions 64 of armature 24 extend, the outer peripheral surfaces 90 of portions 64 defining fixed airgaps 92 with bridging section 88.

Inlet conduit member 26 is formed of suitable magnetic material and has flange portion 94 at its front end 96 abutting shoulder 98 on the rear side of flange portion 72 of bobbin member 18. Rear end 100 of rear portion 78 of easing member 20 is crimped to the outer periphery of flange portion 94 thereby holding nozzle member 14 and bobbin 18 with coil 32 thereon in assembled relation. Inlet conduit member 26 and easing member 80 form a complete casing for the valve assembly 12.

Core 22 formed of magnetic material is positioned within opening 68 of barrel portion 66 of bobbin l8 and is spaced from the wall thereof. Core 22 has front end 102 which defines adjustable airgap 104 with armature 24 when valve plunger 16 is in its closed position. Rear end 106 of core 22 is threadedly engaged with front end 108 of core mounting member 28 by means of external threads 109, as shown. Rear end 110 of core mounting member 28 is threadedly engaged with front end 96 of inlet conduit 26 by means of external threads 154, as shown.

It will be seen that cut-out portions 62 of armature 24 define, with fingers 44, second fluid passages 112 which communicate with first fluid passages 52. A third fluid passage 114 is defined between core 22 and front portion 108 of core mounting member 28, and central opening 68 in barrel portion 66 of bobbin 18. Core mounting member 28 has a central opening 116 and opening 118 communicates between opening 116 and passage 114. Interior 120 of inlet conduit 26 communicates with opening 1 16 in core mounting member 28. O-ring seal 122 is positioned between rear end 124 of barrel portion 66, shoulder 98, flange portion 94 and core'mounting member 28, as shown.

Coil spring 126 surrounds core member 22 and acts between armature 24 and the end of front portion 108 of core mounting member 28. Spring 126 thus biases armature 24 and valve plunger 16 forwardly to the closed position thereby causing front end 48 to engage valve seat 42 so as to close orifice 36.

It will now be seen that rear portion 78, annular wall 128 and bridging section 88 of casing member 20, fixed airgap 92, armature member 24, adjustable airgap 104, core member 22, core mounting member 28, and flange portion 94 of inlet conduit 26 form a magnetic circuit for coil 32, as shown by arrows 130. Thus, upon energization of coil 32, armature 24 is attracted toward front end 102 of core member 22 thereby moving valve plunger 16 rearwardly so that front end 48 moves away I from valve seat 42 so as to open orifice 36. Thus, with coil 32 energized thereby moving valve plunger 16 to its open position, fluid under pressure in inlet conduit 26 will flow through openings 116 and 118 in core mounting member 28, and passages 114, 112 and 52 to and through orifice 36, as shown by arrows 132.

Rear end 134 of inlet conduit 26 is adapted to receive inlet hose 136, as shown. A suitable filter, shown in dashed lines at 138, may be positioned in inlet conduit 26, as shown. Flange 94 of inlet conduit 26 has opening therein in which insulator 142 is seated,

insulator 142 carrying a pair of conventional knife terminals 144 to which leads 146 to coil 32 are connected. Conventional plug 148 is adapted to receive knife terminals 144.

In order selectively to adjust the width of adjustable airgap 104 and thus to control the area of the orifice and the rate of pick-up of armature 24, rear end 106 of core member 22 is provided with screwdriver slot 150. It will be seen that a screwdriver or other suitable tool may be inserted through the interior of inlet conduit 26 at any time after final assembly of valve 12 and be engaged with screwdriver slot 150, used to retract or extend core 22 thereby to make adjustable airgap 104 wider or narrower, as desired.

In order selectively to adjust the spring rate of coil spring 126 and thus to adjust the dropout rate of armature 24, screwdriver slot 152 is formed in rear end 110 of core mounting member 28. Thus, in similar fashion, a screwdriver or other suitable tool may be inserted through inlet conduit 26 and by engagement with screwdriver slot 152, used to retract or extend core mounting member 28 thus to compress or extend spring 126.

It will bereadily seen in the event adjustment of the spring rate of spring 126 is not desired, external threads 154 on core mounting member 28 and the cooperating internal threads on inlet conduit 26 may be eliminated, and core mounting member 28 secured to inner end 96 of inlet conduit 26 by crimping or brazing, adjustment of airgap 104 being retained by the threaded engagement of rear end 106 of core 22 with front end 108 of core mounting member 28.

Referring now to FIG. 6 in which like elements are indicated by like reference numerals and similar elements by primed reference numerals, here inlet conduit 26' has front portion 154 extending into opening 68 in barrel portion 66 of bobbin 18. Flange member 156 formed of magnetic material has hub portion 158 engaging rear portion 160 of inlet conduit 26 and crimped thereto, as at 162. The front end of hub 158 engages O-ring seal 122., flange 156 engages shoulder 98' of bobbin 18, and rear end 100 of rear portion 78 of casing 20 is crimped to the outer periphery of flange 156, as shown.

A plurality of radially spaced projections 164 adjacent the front end of front portion 154 of inlet conduit 26' engage and locate front end 102 of core 22. Core 22' is spaced from the inner wall of front portion 154 of inlet conduit 26' thereby forming passage 114'. Enlarged portion 166 is formed on rear end 106 of core 22' and has indentations 168 formed therein. Rear portion 161) of inlet conduit 26' is crimped in certain of the indentations 168, as at 170, and the remaining indentations 168 communicate between opening 120' in inlet conduit 26 andpassage 114' (FIGS. 9 and Here, valve plunger 16' has central opening 172 formedtherein having front end 174. Armature 24'. is secured to rear end 60 of valve plunger 16' by annular shoulder. 176 seated in and adhesively secured to recess 178. Armature 24 has central opening 180 therethrough communicating with opening 172 in valve plunger 16. Coil spring 126' is seated in openings 172, 180 and acts between end 174 of opening 172 and front end 102 of core 22'. Front end 102' of core 22 defines airgap 184 with armature 24'.

In this embodiment, fingers 44' extend forwardly from front end 74 of barrel portion 66 of bobbin 18 and engage rear end 46' of body portion 37 of nozzle member 14'.

Flange 156 has opening 140' therein through which insulator portion 182, formed integrally with rear flange portion 72 of bobbin 18, extends. Knife terminals 144' are molded in insulator portion 182 and have coil leads 146' connected thereto, as shown.

It will be seen that rear portion 78, front wall 128' and bridging section 88 of casing fixed airgap 92', armature member 24', airgap 184, core 22', front portion 154 of inlet conduit 26', hub portion 158 and flange 156 form the magnetic circuit for coil 32' so that, upon energization of coil 32', armature 24' is attracted toward end 102' of core 22 thus moving valve plunger 16' rearwardly to its open position. In the open position, fluid under pressure in inlet conduit 26 will flow through indentations 168, passage 114, passages 94', and passages 52 to and out of orifice 36, as shown by arrows 132'. It will be seen that in this embodiment, adjustment of airgap 184 is accomplished upon initial assembly, being determined by the location of the crimped connection 170 of core portion 166 to inlet conduit 26.

While these have been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

l. A solenoid valve comprising: a hollow nozzle member formed of non-magnetic material and having a front end with a discharge orifice formed therein, and an open rear end; a bobbin member formed of nonmagnetic material and including .a hollow barrel portion having open front and rear ends, and spaced flange portions formed on said barrel portion, said nozzle member and said barrel portion being in alignment with said rear end of said nozzle member spaced from said front end of said barrel portion; a coil surrounding said barrel portion between said flange portions; a valve plunger in said nozzle member axially movable between closed and open positions and having a front end which closes said orifice in said closed position, and a rear end, said plunger forming a first fluid passage communicating with said orifice in said open position; casing means formed of magnetic material and surrounding a part of said nozzle member and said bobbin member and coil for holding said nozzle member and bobbin member in assembled relation, said casing means having a portion bridging the space between said rear end of said nozzle member and said front end of said barrel portion of said bobbin member;

a disc armature member formed of magnetic material at said rear end of said plunger and movable-therewith, said armature having a portion extending into said space defining a first, fixed airgap with said casing means bridging portion, saidarmature forming a second fluid passage communicating with said first passage; a core member formed of magnetic material in said barrel portion and forming a second airgap with said armature in said closed position; said core member, casing means and armature forming a magnetic circuit for said coil whereby said armature is moved toward said core and said plunger is moved to said open position upon energization of said coil, said core forming a third fluid passage communicating with said second fluid passage; spring means normally biasing said armature and plunger to said closed position;

' and means for securing said core to said casing means;

a plurality of portions respectively extending between said fingers.

4. The valve of claim 1 wherein said plunger is at least partially spaced from the interior wall of said nozzle thereby forming said first passage, said armature having recesses formed in said portion thereby forming said second passage, said core being at least partially spaced from the interior wall of said barrel portion thereby forming said third passage.

5. The valve of claim 1 wherein said securing means secures said core to said inlet conduit.

6. The valve of claim 5 wherein said core is elongated and has front and rear ends with said front end forming said second airgap, said securing means being adjacent said rear end of said core. I

7. The valve of claim 6 further comprising means for adjustably connecting said core to said securing means thereby selectively to adjust said second airgap.

8. The valve of claim 7 wherein said connecting means comprises a threaded connection.

9. The valve of claim 6 wherein said core is spaced from the interior wall of said barrel portion thereby forming a part of said third passage, said securing means having the remaining part of said third passage formed therein.

10. The valve of claim 9 wherein said spring means is a coil spring surrounding said core and acting between said armature and said securing means.

11. The valve of claim 10 further comprising means for adjustably connecting said securing means to said inlet conduit thereby selectively to adjust the spring rate of said spring.

12. The valve of claim 11 wherein said connecting means comprises a threaded connection.

13. The valve of claim 10 wherein said securing meanscomprises a sleeve having a front portion extending into said barrel portion and a rear portion extending into said inlet conduit, said spring acting against said front end of said sleeve, said rear end of said sleeve having a threaded connection with said inlet conduit thereby selectively to adjust the spring rate of said spring, said rear end of said core having a threaded connection with said frontend of said sleeve thereby selectively to adjust said second airgap.

14. The valve of claim 1 wherein said inlet conduit has a front portion extending into said barrel portion and a rear portion, said core being within and spaced from said inlet conduit thereby forming said third passage, said core being elongated and having front and rear ends, said frontend of said core forming said second airgap, said securing means being formed on said rear end of said core and being connected to said rear portion of said inlet conduit.

15. The valve of claim l4 wherein said front portion of said inlet conduit has spaced projections thereon engaging and supporting said front end of said core.

16. The valve of claim 14 wherein said securing means comprises an enlarged portion formed on said rear end of said core, said enlarged portion having indentations in its outer periphery communicating between said third passage and said rear portion of said inlet conduit, said rear portion of said inlet conduit being crimped to said enlarged portion.

17. The valve of claim 1 wherein said armature has a central opening formed therethrough said plunger member havlng a central openlng formed in its rear end communicating with said armature opening, said plunger opening having a front end, said core having a front end forming said second airgap with said armature, said spring means comprising a coil spring in said openings acting between said front end of said plunger opening and said front end of said core. 

1. A solenoid valve comprising: a hollow nozzle member formed of non-magnetic material and having a front end with a discharge orifice formed therein, and an open rear end; a bobbin member formed of non-magnetic material and including a hollow barrel portion having open front and rear ends, and spaced flange portions formed on said barrel portion, said nozzle member and said barrel portion being in alignment with said rear end of said nozzle member spaced from said front end of said barrel portion; a coil surrounding said barrel portion between said flange portions; a valve plunger in said nozzle member axially movable between closed and open positions and having a front end which closes said orifice in said closed position, and a rear end, said plunger forming a first fluid passage communicating with said orifice in said open position; casing means formed of mAgnetic material and surrounding a part of said nozzle member and said bobbin member and coil for holding said nozzle member and bobbin member in assembled relation, said casing means having a portion bridging the space between said rear end of said nozzle member and said front end of said barrel portion of said bobbin member; a disc armature member formed of magnetic material at said rear end of said plunger and movable therewith, said armature having a portion extending into said space defining a first, fixed airgap with said casing means bridging portion, said armature forming a second fluid passage communicating with said first passage; a core member formed of magnetic material in said barrel portion and forming a second airgap with said armature in said closed position; said core member, casing means and armature forming a magnetic circuit for said coil whereby said armature is moved toward said core and said plunger is moved to said open position upon energization of said coil, said core forming a third fluid passage communicating with said second fluid passage; spring means normally biasing said armature and plunger to said closed position; and means for securing said core to said casing means; said casing means including an inlet conduit portion communicating with said third passage whereby fluid flows from said inlet conduit through said passages and orifice upon energization of said coil.
 2. The valve of claim 1 further comprising means on a respective end of one of said nozzle member and barrel portion and engaging the other for forming said space.
 3. The valve of claim 2 wherein said space forming means comprises spaced fingers, said armature having a plurality of portions respectively extending between said fingers.
 4. The valve of claim 1 wherein said plunger is at least partially spaced from the interior wall of said nozzle thereby forming said first passage, said armature having recesses formed in said portion thereby forming said second passage, said core being at least partially spaced from the interior wall of said barrel portion thereby forming said third passage.
 5. The valve of claim 1 wherein said securing means secures said core to said inlet conduit.
 6. The valve of claim 5 wherein said core is elongated and has front and rear ends with said front end forming said second airgap, said securing means being adjacent said rear end of said core.
 7. The valve of claim 6 further comprising means for adjustably connecting said core to said securing means thereby selectively to adjust said second airgap.
 8. The valve of claim 7 wherein said connecting means comprises a threaded connection.
 9. The valve of claim 6 wherein said core is spaced from the interior wall of said barrel portion thereby forming a part of said third passage, said securing means having the remaining part of said third passage formed therein.
 10. The valve of claim 9 wherein said spring means is a coil spring surrounding said core and acting between said armature and said securing means.
 11. The valve of claim 10 further comprising means for adjustably connecting said securing means to said inlet conduit thereby selectively to adjust the spring rate of said spring.
 12. The valve of claim 11 wherein said connecting means comprises a threaded connection.
 13. The valve of claim 10 wherein said securing means comprises a sleeve having a front portion extending into said barrel portion and a rear portion extending into said inlet conduit, said spring acting against said front end of said sleeve, said rear end of said sleeve having a threaded connection with said inlet conduit thereby selectively to adjust the spring rate of said spring, said rear end of said core having a threaded connection with said front end of said sleeve thereby selectively to adjust said second airgap.
 14. The valve of claim 1 wherein said inlet conduit has a front portion extending into said barrel portion and a rear portion, said core being within and spaced from said inlet conduit thereBy forming said third passage, said core being elongated and having front and rear ends, said front end of said core forming said second airgap, said securing means being formed on said rear end of said core and being connected to said rear portion of said inlet conduit.
 15. The valve of claim 14 wherein said front portion of said inlet conduit has spaced projections thereon engaging and supporting said front end of said core.
 16. The valve of claim 14 wherein said securing means comprises an enlarged portion formed on said rear end of said core, said enlarged portion having indentations in its outer periphery communicating between said third passage and said rear portion of said inlet conduit, said rear portion of said inlet conduit being crimped to said enlarged portion.
 17. The valve of claim 1 wherein said armature has a central opening formed therethrough said plunger member having a central opening formed in its rear end communicating with said armature opening, said plunger opening having a front end, said core having a front end forming said second airgap with said armature, said spring means comprising a coil spring in said openings acting between said front end of said plunger opening and said front end of said core. 